Scheduling system and scheduling method for the same

ABSTRACT

A schedule management table is additionally provided in a scheduling system comprising: a time slot for specifying, in slots, the cell transfer sequence of individual lines in one turn; a cell read sequence management table having elements to which the lines are set as cell transfer objects; schedule computation means for controlling the setting of the lines to the cell read sequence management table; and allocation processing means for converting the elements of the cell read sequence management table to specified positions of the slots in the time slot. The schedule management table indicates positions, within the cell read sequence management table, to which transfer object lines are newly set, for each PCR (peak cell rate) value. The scheduling system can reduce the necessity of update of the cell read sequence management table and can execute data transfer which assures the rate of each ATM line.

FIELD OF THE INVENTION

[0001] The invention relates to the control of cell read in an ATM(asynchronous transfer mode) line, and more particularly to a schedulingsystem for efficiently reading each cell and a scheduling method for thesame.

BACKGROUND OF THE INVENTION

[0002] ATM (asynchronous transfer mode) is a communication system forsending or receiving at a high speed all data, to be transmitted, whichhave been divided into units called “cells” of 53 octets (one octet=8bits) ATM is suitable for the transfer of large-capacity data, such asmultimedia data, and constitutes a basic technique of broadband ISDN.

[0003] In ATM, multiplex communication is carried out, and, in addition,the transmission rare can be regulated at a desired value by setting thenumber of cells sent per given time (cell rate) to a desired value. Byvirtue of this, even when voices (audio), static images, moving imagesand the like are present together in an object to be sent, the objectcan be properly transmitted.

[0004] An ATM switch performs large-capacity, high-speed digitalswitching and mediates communication between terminals. An example ofswitching conducted by the ATM switch is to cell multiplex a pluralityof ATM lines into a single physical transmission path followed by sendof the multiplexed cells.

[0005] In this case, regarding the sequence of read of data in each ATMline (i.e., the sequence of send of cell in each line), also from theviewpoint of sending data at a proper speed, in sending cells, theindividual cells should be dispersed, if possible, at equal spacings, soas to avoid the send of cells in the concentrated state at a time in thesame line according to the rate of each line.

[0006] For example, in the control of send of cells using a time slotfor designating the sequence of send of the individual cells, forexample, in order to reduce a burst property at an output port in eachATM line, scheduling should be carried out to properly allocate theindividual cells in the same line to respective positions dispersedwithin the time slot.

[0007] For each line, PCR (peak cell rate) is used as a value fordesignating the maximum speed for sending the cells in the line. PCRindicates the maximum speed at which cells can be transferred in ATM.Further, the minimum spacing for transferring the cells in the same lineis determined by the PCR value. Hereinafter, the term “PCR value” in thepresent specification is used for indicating the number of cells whichcan be transferred within one time slot in each line. That is, forexample, in a line such that the PCR value is “4,” four cells can besent per turn of the time slot.

[0008] An example of a conventional technique for allocating cells ineach line respectively to positions dispersed within the time slot willbe explained. FIG. 4 is a diagram illustrating an example of aconventional scheduling technique for allocating individual cellsrespectively to positions dispersed within a time slot, wherein thelength of the time slot is 16.

[0009] At the outset, a cell read sequence management table is providedwhich is a table having a length corresponding to the maximum number ofcells allocable to the time slot (hereinafter, this number of cells isreferred to as “TEN”).

[0010] Elements, the number of which is equal to the number of cellstransferred within one time slot in each data to be transferred (thatis, corresponding to the PCR value of each data), are ensured togetherwithin the cell read sequence management table. In the example shown inFIG. 4, the PCR value of ATM lines (or data to be transferred) indicatedby “A” and “B” is “2,” the PCR value of “C” is “1,” and the elements aresuccessively ensured from the head element within the cell read sequencemanagement table.

[0011] In the time slot, slots respectively to which the cells areallocated are designated corresponding to the sequence of individualelements in the cell read sequence management table, and the cells ineach line to be sent are allocated respective to the designatedpositions. In the example shown in FIG. 4, the cells of “A” areallocated to slots corresponding to numbers 1 and 2, and the cells of“B” are allocated to slots corresponding to numbers 3 and 4.

[0012] In the time slot, the cells allocated to the respective slots aresuccessively sent clockwise. That is, in the sequence in the cell readsequence management table, 1, 9, 5, 13, . . . are sent in that order.Thus, the cells in the same line are sent in the dispersed state. Forexample, in FIG. 4, the two cells in “A” or “B” are allocated topositions which face each other within the time slot. Therefore, at arate for sending the two cells in one turn, the cells are successivelysent at equal spacing.

[0013] Thus, scheduling of the cell read sequence management table basedon the PCR value in each ATM line in a service object followed by thecontrol of read according to the scheduled call read sequence managementtable can ensure the transfer rate in the transfer of each cell in eachATM line of the service object.

[0014] Successive positions in the sequence within the cell readsequence management table can be converted to respective positionsdispersed within the time slot, for example, by the following method.

[0015]FIG. 2 shows an example of calculation in a method for convertingthe positions of the cell read sequence management table to respectivepositions within the time slot, and FIG. 3 shows a list of the resultsof the conversion.

[0016] In this example, a time slot length of 16 is taken as an example.The same is true of other cases where the length is a value obtained byraising 2 to the nth power wherein n is an integer (for example, 32, 64,. . . etc.). Here the length of the cell read sequence management tableis equal to the length of the time slot, and thus can be expressed interms of binary number of which the number of digits is calculated byequation log 2 L wherein L is the length of the table. In this example,log 2 (16)=4 (digits).

[0017] As shown in FIG. 2, “1” is first subtracted from each value inthe sequence, and the value thus obtained is expressed in terms ofbinary number of four digits. The numerical values (“0” or “1”) of theindividual digits expressed in terms of binary number are converted soas to be reversed in sequence. That is, MSB (most significant bit) sideand LSB (least significant bit) side in the value expressed in terms ofbinary number of four digits are reversed in sequence to obtain a newbinary number. “1” is added to the binary number thus obtained todetermine a value which is regarded as the corresponding time slotposition.

[0018] For example, in the “8th” within the cell read sequencemanagement table, the subtraction of “1” from this value followed by theexpression of the obtained value in terms of a four-digit binary numbergives “0111” (=7). These individual digits are rearranged so as to bereversed in sequence to give a value of “1110” (=14). Finally, “1” isadded to this value to obtain the corresponding time slot position “15”as the conversion result.

[0019] Here values obtained by raising 2 to the nth power, wherein n isan integer, are used as the maximum rate (PCR value) of the band in eachservice ATM line, and the cell read sequence management table isscheduled based on the PCR values. The use of values obtained by raising2 to the nth power. wherein n is an integer, (i.e., 1, 2, 4, 8, . . .etc.) as the PCR value is common in the art. In this method, theproperties of the binary number can be utilized, and the processing canbe simplified.

[0020] In particular, this conversion method is suitable in the casewhere, in the cell read sequence management table, elementscorresponding to the PCR value (value obtained by raising 2 to the nthpower wherein n is an integer) are continuously ensured from a positionwhich is one ahead of the position corresponding to a value obtained bymultiplying the PCR value by an integer, that is, a position which isnext to the position corresponding to a value obtained by multiplyingthe PCR value by an integer. The elements, which have been ensured here,are dispersed at equal spacings in the time slot. Further, ensuring theelements corresponding to the PCR value (value obtained by raising 2 tothe nth power wherein n is an integer) from one ahead of the positioncorresponding to a value obtained by multiplying the PCR value by aninteger can be simply achieved by arranging the elements correspondingto the PCR value in each line in the descending order of the PCR valuesfrom the head.

[0021] For example, in the example shown in FIG. 4, the three lines “A,”“B,” and “C” having respective PCR values of “2,” “2,” and “1” aresuccessively arranged in the descending order of the PCR values toensure the elements corresponding to the PCR values in the cell readsequence management table. This permits the elements to be allocated atequal spacings to the time slot, whereby cells in each line are sent atequal intervals.

[0022] Further, to the contrary, in the prior art, in order to transfercells sent from each line at an even rate, in the cell read sequencemanagement table, the elements for each line are successively arrangedso that the PCR values are in descending order by the above method.

[0023] In the ATM switch which transfers cells in each of the ATM lines,however, data is not always sent at a stationary data transfer rate.That is, in some cases, the transfer of data is ended halfway in eachline, or, on the contrary, in some cases, in each line, new datatransfer is started.

[0024] For this reason, in the conventional ATM switch, as describedabove, the individual lines are scheduled from the head of the cell readsequence management table in the descending order of PCR values and, atthe same time, so as to avoid the occurrence of an unused idle areabetween lines, and the positions of each line within the cell readsequence management table are properly updated.

[0025] Next, a conventional scheduling system will be explained whereina cell read sequence management table is scheduled by the above method.

[0026]FIG. 6 is a block diagram showing the construction of a schedulingsystem 100 a for controlling the read of cells in a conventional ATMline.

[0027] Referring now to FIG. 6, in a conventional scheduling system 100a, data received in a line setting interface 10 is first supplied to aschedule computation section 20 a, and calculation for scheduling of thecell read management table is executed.

[0028] An allocation processor 30 sets, in a time slot 40, the result ofscheduling calculated by the schedule computation section 20 a. In otherwords, the allocation processor 30 converts the individual elements inthe cell read management table to respective positions in the time slot40 by the conversion method shown in FIGS. 2 and 3.

[0029] Shaping service, which has assured the rate of each ATM line, canbe carried out by reading an ATM line, input into the device, from aconnection input queue 50 to a shaping service output queue 60 accordingto the time slot setting.

[0030] The construction and operation of the conventional schedulecomputation section 20 a shown in FIG. 6 are as follows.

[0031] Specifically, data sent from the line setting interface 10 isprocessed in a parameter processor, and is output to a schedule objectcomputation section. Upon new receive of line or delete of line, theschedule object computation section computes a line, in the cell readsequence management table, of which the position is to be changed. Inthe conventional schedule computation section 20, ATM lines as theschedule change object are a part of lines having the same PCR value asPCR values of lines, of which a line is to be newly received or deleted,and all of lines having a smaller PCR value.

[0032] A schedule clear section clears the cell read sequence managementtable of which the schedule is to be changed. The schedule computationsection performs scheduling in the descending order of PCR values oflines (i.e., a line having a larger PCR value among the lines as thecomputed schedule change object is scheduled in an earlier stage) in asuccessive manner from the head of idle areas in the cell read sequencemanagement table. The reason for this is that scheduling in thedescending order of PCR values of lines can provide better receiveefficiency of the cell read sequence management table from the viewpointof assuring the rate of ATM lines to be shaped.

[0033] Further, as described above, when PCR values are values obtainedby raising 2 to the nth power, wherein n is an integer, scheduling inthe descending order of PCR values of lines (i.e., a line having alarger PCR value is scheduled in an earlier stage) from the head of idleareas in the cell read sequence management table can ensure positionsassuring the rate in the cell read management table.

[0034] Here when lines have not been aligned, that is, when theindividual lines have been successively scheduled from the head in idleareas of the cell read sequence management table without alignment,however, the arrangement of lines in the descending order is broken and,consequently, there is a fear of the assurance of line rate being lost.

[0035]FIG. 5 is a diagram illustrating the read of cells in the casewhere the arrangement of lines in descending order in a cell readsequence management table has been broken, In FIG. 5, three lines shownin FIG. 4 are arranged in the order of “C,” “A,” and “B,” that is, inthe order of PCR values “1,” “2,” and “2.” Unlike the example of FIG. 4in which cells have been sent at equal intervals, in the lines “A” and“B” cells are sent at uneven intervals which do not satisfy a sendinterval requirement indicated by the PCR value.

[0036] Therefore, in the prior art, when a schedule is newly received orchanged, as described above, the individual lines as the processingobject should be aligned.

[0037] As described above, in the conventional scheduling system, everytime when a change has occurred in a line to be cataloged in the cellread sequence management table, troublesome processing should be carriedout such that all the cataloged lines are aligned in the descendingorder of PCR values and rearranged from the head.

[0038] An example of a conventional measure devised to deal with thisproblem is as follows. In order that, among lines cataloged in the cellread sequence management table, lines having a larger PCR value than thePCR value of the line, in which the change has occurred do not undergo achange in the position within the cell read sequence management tableupon the rescheduling, the object of the position conversion processingis limited only to a part of lines having the same PCR value as the PCRvalue of the line, in which the change has occurred, and all the lineshaving smaller PCR values than the line, in which the change hasoccurred, followed by computation of rescheduling. Even when the objectof the rescheduling is limited to a narrower range in this way, however,there remains the necessity of executing troublesome processing suchthat, every time when a change, such as new addition of a line, hasoccurred, the lines are aligned and rearranged.

SUMMARY OF THE INVENTION

[0039] Accordingly, it is a first object of the invention to provide ascheduling system, which can solve the above problems of the prior artand, without requiring, for example, complicate construction andcomplicate processing, can assure the rate of each line and can executehigh-speed, high-capacity data transfer, and a scheduling method forsaid scheduling system.

[0040] It is a second object of the invention to provide a schedulingsystem, which can solve the above problems of the prior art and cansignificantly reduce the necessity of update of the cell read sequencemanagement table through the provision of an additional table forproperly managing and updating positions of individual lines within thecell read sequence management table, and a scheduling method for saidscheduling system.

[0041] According to the first feature of the invention, a schedulingsystem comprises:

[0042] a time slot for specifying the transfer sequence of individuallines in one turn, in which each cell is transferred, in slotsindicating respective points in the turn:

[0043] a cell read sequence management table which has elements in thesame number as the number of slots provided in the time slot and setsthe lines as cell transfer objects to the elements;

[0044] schedule computation means for controlling the setting of thelines to the cell read sequence management table;

[0045] allocation processing means for converting the elements of thecell read sequence management table respectively to specified positionsof the slots in the time slot; and

[0046] a schedule management table for indicating positions, within thecell read sequence management table, to which transfer object lines arenewly set, for each PCR value of the lines, said PCR value being thenumber of cells, transferred from the line, per cell transfer turn andrepresenting the cell send rate of each line,

[0047] the specified line cells being successively transferred for eachturn according to the sequence specified in the time slot,

[0048] the cell read transfer sequence in each line being controlledaccording to the cell send rate in each of the lines.

[0049] In the scheduling system according to the first feature of theinvention, the schedule computation means preferably comprises:

[0050] means which, when a requirement is satisfied such that there isan idle element, in the cell read sequence management table, which islocated one element ahead of a position of an element corresponding to avalue obtained by multiplying the specified PCR value by an integer, andthe contemplated line can be set to continuous elements starting fromthe idle element and corresponding to the specified PCR value and, inaddition, when an element is present in the heading area of thecontinuous elements, functions to catalog the position of said element,which is located one element ahead of a position of an elementcorresponding to a value obtained by multiplying the specified PCR valueby an integer, as data indicating the set position of the line havingthe specified PCR value, in relation with the PCR value in the schedulemanagement table;

[0051] means which, when a line to be newly transferred has occurred,newly sets the line to continuous elements corresponding to the PCRvalue of the line, in the cell read sequence management table, from theset position corresponding to the PCR value of the line recorded in theschedule management table;

[0052] means which, when the communication of a line being currentlytransferred has been deleted, cancels the setting of the line from theelement, in the cell read sequence management table, to which the linehas been set; and

[0053] means which, when new setting or delete of a transfer object linehas occurred, updates the catalog of the schedule management table.

[0054] In the scheduling system according to the first feature of theinvention, the allocation processing means preferably comprises:

[0055] means which converts the elements within the cell read sequencemanagement table, to respective specified positions within the timeslot, based on the designation of the slot position as the conversiondestination for each element specified in such a manner that thecontinuous elements corresponding to the PCR value, that have beenensured from a position which is one element ahead of a position of anelement corresponding to a value obtained by multiplying the PCR valueby an integer, in the cell read sequence management table are convertedto respective positions dispersed at equal spacings in the time slot;and

[0056] means which, when a line is in the state of being set to elementsin the cell read sequence management table, performs specifying andsetting, in a slot as the conversion destination of the line in the timeslot, so as to transfer cells of the line.

[0057] In the scheduling system according to the first feature of theinvention, preferably, the number of slots in the time slot and the PCRvalue of each of the lines each are a value obtained by raising “2” tothe nth power, therein n is a non-negative integer.

[0058] In the scheduling system according to the first feature of theinvention, preferably,

[0059] the conversion from the cell read sequence management table tothe time slot is carried out by a method comprising the steps of:

[0060] raising “2” to the “Ath” power, wherein “A” is an integer, toprovide a value as the length of the time slot;

[0061] indicating the positions of the individual elements in the cellread sequence management table and the slot positions of the time slotby using continuous numbers from “1” to the is value of the time slotlength;

[0062] taking each element from the cell read sequence management table;

[0063] subtracting “1” from the value of the continuous numbers in theelement and expressing the obtained value in terms of binary number of“A” digits while, when a high order value is absent, supplementing “0”;

[0064] converting the numerical values of the “A” digits expressed interms of binary number so as to be reversed in sequence with respect tothe arrangement from higher order digit to lower order digit to providea converted binary number of “A” digits; and

[0065] adding “1” to the value of the converted binary number of “A”digits to determine a value as a slot position, in the time slot, whichis the element conversion destination.

[0066] In the scheduling system according to the first feature of theinvention, preferably, the schedule computation means performs afunction such that, upon the cancellation of the setting of a line fromthe elements in the cell read sequence management table, if another linehaving a smaller PCR value than said line is in the state or being setto a position behind the position to which the said line has been set,the set position of said another line is moved to the position fromwhich the setting of said line has been cancelled.

[0067] In the scheduling system according to the first feature of theinvention, preferably, the schedule computation means performs afunction such that, upon the cancellation of the setting of a line fromthe elements in the cell read sequence management table, if other lineshaving a smaller PCR value than said line are in the state of being setto positions behind the position to which the said line has been set,the set position of one line, which has the largest PCR value in saidother lines and is located in the rearmost position of said other lines,is moved to the position from which the setting of said line has beencancelled.

[0068] In the scheduling system according to the first feature of theinvention, the line may be an ATM line.

[0069] According to the second feature of the intention, a schedulingmethod comprises the steps of:

[0070] indicating the send rate of cells in each line in terms of PCRvalue which is the number of cells, transferred from the line, per celltransfer turn;

[0071] successively transferring cells of a specified line according tothe sequence specified in slots, in a time slot for specifying thetransfer sequence of individual lines in the cell transfer turn,indicating each point in the turn;

[0072] controlling the setting of each line in a sell read sequencemanagement table which has elements in the same number as the number ofslots provided in the time slot and sets the lines as cell transferobjects to the elements;

[0073] converting the individual elements in the cell read sequencemanagement table to respective specified slot positions in the timeslot; and

[0074] properly updating and making reference to a schedule managementtable which indicates positions, within the cell read sequencemanagement table, to which transfer object lines are newly set, for eachPCR value of the lines,

[0075] the cell read transfer sequence in each line being controlledaccording to the cell send rate in each of the lines.

[0076] The scheduling method according to the second feature of theinvention may further comprise the steps of:

[0077] when a requirement is satisfied such that there is an idleelement, in the cell read sequence management table, which is locatedone element ahead of a position of an element corresponding to a valueobtained by multiplying the specified PCR value by an integer, and thecontemplated line can be set to continuous elements starting from theidle element and corresponding to the specified PCR value and, inaddition, when an element is present in the heading area of thecontinuous elements, cataloging the position of said element, which islocated one element ahead of a position of an element corresponding to avalue obtained by multiplying the specified PCR value by an integer, asdata indicating the set position of the line having the specified PCRvalue within the cell read sequence management table, in relation withthe PCR value in the schedule management table;

[0078] when a line to be newly transferred has occurred, newly settingthe line to continuous elements corresponding to the PCR value of theline, in the cell read sequence management table, from the set positioncorresponding to the PCR value of the line recorded in the schedulemanagement table;

[0079] when the communication of a line being currently transferred hasbeen deleted, canceling the setting of the line from the element, in thecell read sequence management table, to which the line has been set; and

[0080] when new setting or delete of a transfer object line hasoccurred, updating the catalog of the schedule management table.

[0081] The scheduling method according to the second feature of theinvention may further comprise the steps of:

[0082] converting the elements within the cell read sequence managementtable, to respective specified positions within the time slot, based onthe designation of the slot position as the conversion destination foreach element specified in such a manner that the continuous elementscorresponding to the PCR value, that have been ensured from a positionwhich is one element ahead of a position of an element corresponding toa value obtained by multiplying the PCR value by an integer, in the cellread sequence management table are converted to respective positionsdispersed at equal spacings in the time slot; and

[0083] when a line is in the state of being set to elements in the cellread sequence management table, performing specifying and setting, in aslot as the conversion destination of the line in the time slot, so asto transfer cells of the line.

[0084] In the scheduling method according to the second feature of theinvention, preferably, the number of slots in the time slot and the PCRvalue of each of the lines each are a value obtained by raising “2” tothe nth power, wherein n is a non-negative integer.

[0085] In the scheduling method according to the second feature of theinvention, preferably,

[0086] the conversion from the cell read sequence management table tothe time slot is carried out by a method comprising the steps of:

[0087] raising “2” to the “Ath” power, wherein “A” is an integer, toprovide a value as the length of the time slot;

[0088] indicating the positions of the individual elements in the cellread sequence management table and the slot positions of the time slotby using continuous numbers from “1” to the value of the time slotlength;

[0089] taking each element from the cell read sequence management table;

[0090] subtracting “1” from the value of the continuous numbers in theelement and expressing the obtained value in terms of binary number of“A” digits while, when a high order value is absent, supplementing “0”;

[0091] converting the numerical values of the “A” digits expressed interms of binary number so as to be reversed in sequence with respect tothe arrangement from higher order digit to lower order digit to providea converted binary number of “A” digits; and

[0092] adding “1” to the value of the converted binary number of “A”digits to determine a value as a slot position, in the time slot, whichis the element conversion destination.

[0093] In the scheduling method according to the second feature of theinvention, preferably, upon the cancellation of the setting of a linefrom the elements in the cell read sequence management table, if anotherline having a smaller PCR value than said line is in the state of beingset to a position behind the position to which the said line has beenset, the set position of said another line is moved to the position fromwhich the setting of said line has been cancelled.

[0094] In the scheduling method according to the second feature of theinvention, preferably, upon the cancellation of the setting of a linefrom the elements in the cell read sequence management table, if otherlines having a smaller PCR value than said line are in the state ofbeing set to positions behind the position to which the said line hasbeen set, the set position of one line, which has the largest PCR valuein said other lines and is located in the rearmost position of saidother lines, is moved to the position from which the setting of saidline has been cancelled.

[0095] In the scheduling method according to the second feature of theinvention, the line may be an ATM line.

[0096] According to the third feature of the invention, an ATM switchcomprises a scheduling system such that the cell read transfer sequencein each ATM line is controlled according to the cell send rate in eachof the ATM lines, wherein

[0097] said scheduling system

[0098] expresses the cell send rate, in each of the ATM lines, in termsof PCR value, which is the number of cells, transferred from the ATMline, per cell transfer turn and comprises:

[0099] a time slot for specifying the transfer sequence of the ATM linesin one turn, in which each cell is transferred, in slots indicatingrespective points in the turn;

[0100] a cell read sequence management table which has elements in thesame number as the number of slots provided in the time slot and setsthe ATM lines as cell transfer objects to the elements;

[0101] schedule computation means for controlling the setting of the ATMlines to the cell read sequence management table;

[0102] allocation processing means for converting the elements of thecell read sequence management table respectively to specified positionsof the slots in the time slot; and

[0103] a schedule management table for indicating positions, within thecell read sequence management table, to which transfer object ATM linesare newly set, for each PCR value of the ATM lines,

[0104] the specified ATM line cells being successively transferred foreach turn according to the sequence specified in the time slot.

[0105] In the ATM switch according to the third feature of theinvention, preferably, the schedule computation means comprises:

[0106] means which, when a requirement is satisfied such that there isan idle element, in the cell read sequence management table, which islocated one element ahead of a position of an element corresponding to avalue obtained by multiplying the specified PCR value by an integer, andthe contemplated ATM line can be set to continuous elements startingfrom the idle element and corresponding to the specified PCR value and,in addition, when an element is present in the heading area of thecontinuous elements, functions to catalog the position of said element,which is located one element ahead of a position of an elementcorresponding to a value obtained by multiplying the specified PCR valueby an integer, as data indicating the set position of the ATM linehaving the specified PCR value, in relation with the PCR value in theschedule management table;

[0107] means which, when an ATM line to be newly transferred hasoccurred, newly sets the ATM line to continuous elements correspondingto the PCR value of the ATM line, in the cell read sequence managementtable, from the set position corresponding to the PCR value of the ATMline recorded in the schedule management table;

[0108] means which, when the communication of an ATM line beingcurrently transferred has been deleted, the setting of the ATM line iscancelled from the element, in the cell read sequence management table,to which the ATM line has been set; and

[0109] means which, when new setting or delete of a transfer object ATMline has occurred, updates the catalog of the schedule management table.

[0110] In the ATM switch according to the third feature of theinvention, preferably, the allocation processing means comprises:

[0111] means which converts the elements within the cell read sequencemanagement table, to respective specified positions within the timeslot, based on the designation of the slot position an the conversiondestination for each element specified in such a manner that thecontinuous elements corresponding to the PCR value, that have beenensured from a position which is one element ahead of a position of anelement corresponding to a value obtained by multiplying the PCR valueby an integer, in the cell read sequence management table are convertedto respective positions dispersed at equal spacings in the time slot;and

[0112] means which, when an ATM line is in the state of being set toelements in the cell read sequence management table, performs specifyingand setting, in a slot as the conversion destination of the ATM line inthe time slot, so as to transfer cells of the ATM line.

[0113] In the ATM switch according to the third feature of theinvention, preferably, the number of slots in the time slot and the PCRvalue of each of the ATM lines each are a value obtained by raising “2”to the nth power, wherein n is a non-negative integer.

[0114] In the ATM switch according to the third feature of theinvention, preferably,

[0115] the conversion from the cell read sequence management table tothe time slot is carried out by a method comprising the steps of:

[0116] raising “2” to the “Ath” power, wherein “A” is an integer, toprovide a value as the length of the time slot;

[0117] indicating the positions of the individual elements in the cellread sequence management table and the slot positions of the time slotby using continuous numbers from “1” to the value of the time slotlength;

[0118] taking each element from the cell read sequence management table;

[0119] subtracting “1” from the value of the continuous numbers in theelement and expressing the obtained value in terms of binary number of“A” digits while, when a high order value is absent, supplementing “0”;

[0120] converting the numerical values of the “A” digits expressed interms of binary number so as to be reversed in sequence with respect tothe arrangement from higher order digit to lower order digit to providea converted binary number of “A” digits; and

[0121] adding “1” to the value of the converted binary number of “A”digits to determine a value as a slot position, in the time slot, whichis the element conversion destination.

[0122] In the ATM switch according to the third feature of theinvention, preferably, the schedule computation means performs afunction such that, upon the cancellation of the setting of an ATM linefrom the elements in the cell read sequence management table, if anotherATM line having a smaller PCR value than said ATM line is in the stateof being set to a position behind the position to which the said ATMline has been set, the set position of said another ATM line is moved tothe position from which the setting of said ATM line has been cancelled.

[0123] In the ATM switch according to the third feature of theinvention, preferably, the schedule computation means performs afunction such that, upon the cancellation of the setting of an ATM linefrom the elements in the cell read sequence management table, if otherATM lines having a smaller PCR value than said ATM line are in the stateof being set to positions behind the position to which the said ATM linehas been set, the set position of one ATM line, which has the largestPCR value in said other ATM lines and is located in the rearmostposition of said other ATM lines, is moved to the position from whichthe setting of said ATM line has been cancelled.

[0124] BRIEF DESCRIPTION OF THE DRAWINGS

[0125] The invention will be explained in more detail in conjunctionwith the appended drawings, wherein:

[0126]FIG. 1 is a diagram showing an example of conventional schedulingof a cell read sequence management table;

[0127]FIG. 2 is a diagram showing an example of computation in a methodfor converting individual positions in a cell read sequence managementtable respectively to positions within a time slot;

[0128]FIG. 3 is a diagram showing a list of conversion results obtainedby the computation method shown in FIG. 2;

[0129]FIG. 4 is a diagram illustrating an example of scheduling forallocating individual cells respectively to positions dispersed within atime slot;

[0130]FIG. 5 is a diagram illustrating the read of cells in the casewhere the arrangement of lines in descending order has been broken inthe conventional cell read sequence management table;

[0131]FIG. 6 is a block diagram showing the construction of aconventional scheduling system;

[0132]FIG. 7 is a block diagram showing the construction of a schedulingsystem according to a first preferred embodiment of the invention;

[0133]FIG. 8 is a diagram showing an example of a cell read sequencemanagement table in the first preferred embodiment of the invention;

[0134]FIG. 9 is a diagram showing an example of a schedule managementtable in the first preferred embodiment of the invention;

[0135]FIG. 10 is a flow chart illustrating an example of line receiveprocessing in the first preferred embodiment of the invention;

[0136]FIG. 11 is a flow chart illustrating an example of line deleteprocessing in the first preferred embodiment of the invention;

[0137]FIG. 12 is a diagram illustrating an example of update of aparameter for managing idle areas in the first preferred embodiment ofthe invention;

[0138]FIG. 13 is a diagram illustrating an example of computation of aposition correction value with the movement or the position in the firstpreferred embodiment of the invention;

[0139]FIG. 14 is a diagram illustrating an example of the movement of amove object line in the first preferred embodiment of the invention:

[0140]FIG. 15 is a diagram illustrating an example of the correction ofallocation position of a schedule management parameter in the firstpreferred embodiment of the invention; and

[0141]FIG. 16 is a diagram showing an example of scheduling of a cellread sequence management table in the first preferred embodiment of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0142] Preferred embodiments of the invention will be explained indetail in conjunction with the accompanying drawings.

[0143]FIG. 7 is a block diagram showing the construction of a schedulingsystem in a first preferred embodiment of the invention.

[0144] The scheduling system according to this preferred embodiment ofthe invention is a system which manages the sequence of the read ofcalls for each ATM line, for example, in an ATM switch. In this system,each line is properly set in a cell read sequence management table forsetting the sequence of the read of cells, thereby managing the sequenceof the read of cells.

[0145] Further, as explained below, each line is efficiently set in thecell read sequence management table to realize the update of the cellread sequence management table by minimized processing, even in anenvironment such that the receive or delete of lines is repeatedlycarried out.

[0146] Referring now to FIG. 7, a scheduling system 100 according tothis preferred embodiment comprises a line setting interface 10, aschedule computation section 20, an allocation processor 30, and a timeslot 40, and receives a connection input queue 50 and outputs a shapingservice output queue 60. Each of these sections can realize, forexample, using a semiconductor circuit or the like for executing theprocessing of each of the sections. The scheduling system 100 shown inFIG. 7 is different from the conventional scheduling system 100 a shownin FIG. 6 mainly in a schedule computation section 20 and its processingwhich will be explained later.

[0147]FIG. 8 is a diagram showing an example of a cell read sequencemanagement table in the first preferred embodiment of the invention.

[0148] According to the scheduling system in this preferred embodiment,the schedule computation section 20 performs control in such a mannerthat individual lines are ensured, based on PCR values (obtained byraising 2 to the nth power wherein n is an integer), in the cell readsequence management table from its position which is one ahead of theposition corresponding to a value obtained by multiplying the PCR valueby an integer. The ensured individual lines are converted according tothe method for convention to a time slot exemplified in FIGS. 2 and 3,and cells in the lines are read and transferred in the convertedsequence in the time slot. As described above in the column of thebackground of the invention, the elements of the lines ensured from theposition, which is one ahead of the position corresponding to a valueobtained by multiplying the PCR value by an integer, as described abovein connection with the example shown in FIG. 8, are positioned at equalspacings within the time slot, and, thus, proper transfer of cellsaccording to the send rate of each line can be realized.

[0149] When the line can be ensured in a plurality of sites, the line isensured in the first site (the smallest number site). In this case,since a wide unused area is ensured in the rear part of the table,subsequent new lines can be efficiently ensured.

[0150] Here in the conventional scheduling system 100 a, when thereceive or delete of a line has occurred, all the positions of the linesin the cell read sequence management table should be aligned. This isnecessary for properly ensuring the lines from the position which is oneahead of the position corresponding to a value obtained by multiplyingthe PCR value by an integer.

[0151] By contrast, in the scheduling system in the present preferredembodiment, proper line scheduling can be realized, without necessity ofalignment processing, by the provision of a schedule management tableshowing proper allocation positions based on the PCR values of the linesand the arrangement of the lines in designated positions of the table,rather than the adoption of the method wherein the lines are aligned inthe descending order of PCR values.

[0152]FIG. 9 is a diagram showing an example of a schedule managementtable, in the present preferred embodiment, with respect to the exampleof the cell read sequence management table shown in FIG. 8. In FIG, 9,PCR values of lines are shown in the column of “EN,” and properallocation positions corresponding respectively to the PCR values of thelines are shown in the column of “FEP.”

[0153] Here, as described above, the proper allocation positions of thelines in the schedule management table begin from the position which isone ahead of the position corresponding to a value obtained bymultiplying the PCR value of the line by an integer and, at the sametime, has the smallest number.

[0154] The line having a PCR value of “1” can be allocated to the “8th”position of the cell read sequence management table, and the line havinga PCR value of “2” can be allocated to the “15th”, position of the cellread sequence management table. Lines hating a PCR value of “4” or morecannot be allocated to idle areas between other lines and are allocatedfrom the “25th” position which is the final position.

[0155] When a new line has been positioned based on the schedulemanagement table or when a line has been deleted, the schedulecomputation section 20 updates the values in the cell read sequencemanagement table. The update of the schedule management table is muchsimpler than the conventional alignment processing which requires theoperation of the cell read sequence management table per se. Therefore,a significant reduction in processing necessary for scheduling can berealized.

[0156] Thus, in the scheduling system according to this preferredembodiment, the use of the schedule management table permits the linesto be properly ensured from the position, which is one ahead of theposition corresponding to a value obtained by multiplying the PCR valueof the line by an integer, without the necessity of alignment of thecell read sequence management table.

[0157] In the cell read sequence management table in this preferredembodiment, as is apparent from the example shown in FIG. 8, even whenan idle area has occurred between the ensured line areas or even whenthe arrangement in the descending order of PCR values of the cells hasbeen broken, there is no need to execute the processing of alignment ofthe lines.

[0158] When there is an idle area between the ensured line areas,however, the movement of a line in the rear part of the cell readsequence management table so as to fill the idle area permits a widerunused area to be ensured in the rear part. Therefore, such moveprocessing is useful. Accordingly, in an example which is effective inthis preferred embodiment, the following method is considered. At thetime of the delete of a line from the cell read sequence managementtable, when an idle area has occurred between the lines or when the idlearea has been expanded, a search is made for whether or not there is aline, which can fill the idle area, behind the idle area. When thecontemplated line is present, the line is moved into the idle area tofill the idle area or to narrow the idle area. The processing for movingone line in this method is much simpler than the processing for aligningall the lines. Therefore, in addition to the effect of reducingscheduling, the effect of ensuring a wider unused area can be attained.

[0159] In another example, a method is also considered wherein, when aline is newly cataloged in the cell read sequence management table orwhen the line in the above example is moved, only a line having thelongest PCR value, which can be cataloged in the idle area, is catalogedin the idle area between the ensured line areas. That is, in the exampleshown in FIG. 8, a line having a PCR value of “2” can be cataloged inidle areas located at the 15th to 16th positions, and, thus, even whenthe idle area located at the 8th position has already been filled, aline having a PCR value of “1” is cataloged in the 25th position, whichis the final position, rather than the idle area located at the 15thposition. This can be realized, in the same manner as in the aboveexamples, through the determination of each value of the schedulemanagement table by the schedule computation section 20 so as to realizethe above scheduling.

[0160] Next, the operation of an example of the scheduling systemaccording to the present preferred embodiment, including computationprocessing in the schedule computation section 20, will be explained indetail.

[0161] Various parameters, which the schedule computation section 20uses for the computation of schedule, will be first explained.

[0162] As shown in FIG. 7, the internal schedule computation section inthe schedule computation section 20 is provided with a schedulemanagement table. As explained above, the schedule management table is atable which, for each type of PCR value “EN” (here 1, 2, 4, 8), showsthe optimal position “FEP” in the case of the receive of new lines. Thereceive of the individual lines in respective positions indicated inthis table can assure the send rate of the lines.

[0163] Further, the schedule computation section 20 has, as parameters,the total number of entries “TEN” indicating the length of the cell readsequence management table, the total number of used entries “TUEN”indicating the total number of entries, in the cell read sequencemanagement table, to which lines have been allocated, and the final boxnumber “TUEB” indicating the cell read sequence management table in itsrear end to which the line has been allocated. The schedule computationsection 20 manages these values and updates these parameters accordingto the update of the cell read sequence management table.

[0164] For example, in the example shown in FIG. 8, the value of thetotal number of entries “TEN” is “32,” the value of the total number ofused entries “TUEN” is “21,” and the value of the final box number“TUEB” is “24.”

[0165] Further, for the explanation of the processing in the schedulecomputation section 20, “A,” “B,” “C,” “D,” “E,” and “F” each are usedas variables of integers for indicating internal parameters.

[0166]FIG. 10 is a flow chart for explaining processing for newlyreceiving a line within the cell read sequence management tableaccording to the scheduling system in the present example, and FIG. 11is a flow chart for explaining processing for deleting a line fromwithin the cell read sequence management table. In the flow charts, thesquare brackets are used for indicating a value obtained by omittingdecimals of the numerical value within the square brackets (for example,[5/2]=2).

[0167] The operation of the receive of a line will be explained inconjunction with the flow chart shown in FIG. 10.

[0168] In the operation of receive of the line, whether or not theobject line can be received within the cell read sequence managementtable is judged based on the PCR value “EN” of the line to be received.The object line to be received is cataloged in an idle area between thealready cataloged lines or in an unused area at the end.

[0169] At the outset, judgment is made on whether or not an idle area,which can receive a line requested to be received, is present within thealready scheduled cell read sequence management table (step 401).

[0170] When the judgment is such that an idle area corresponding to theobject line is present, corresponding data “FEP” is read from theschedule management table and is decided as an allocation position ofthe line within the cell read sequence management table, followed by theallocation of the line to the position (step 402). This updates the cellread sequence management table, end, hence, the corresponding update isperformed on the schedule management table (step 403).

[0171] In the case where the judgment on the receive of the line in anidle area is such that the line cannot be received in the idle area and,at the same time, the judgment on the receive of the line in an unusedarea in the cell read sequence management table (step 404) is such thatthe line cannot be received (step 405), the receive of the line isjudged to be impossible followed by the end of the line receiveprocessing.

[0172] Here there is a case where, even though the receive of a line inthe idle area is impossible, the allocation of the line to an unusedarea has been judged to be possible. In this case, a position in theunused area, which can receive the line and is suitable for the receiveof the line (that is, a position which is one ahead of the positioncorresponding to a value obtained by multiplying the PCR value by aninteger), is computed (step 406), and is decided as a position forreceiving the object line (step 407). After the decision of the linereceive position, the schedule management table is updated.

[0173] As described in each of the above examples, the schedulemanagement table is updated so that each line is allocated by a desiredmethod. In this example, the schedule computation section 20 executesthe following update processing.

[0174] Parameters for managing a new idle area produced after thereceive of a line are first updated as shown in FIG. 12 (steps 408 to414).

[0175] Specifically, an idle area after the receive of a line iscomputed followed by substitution of the computation result for aparameter “C” (step 408), and the following processing is carried outone by one from lines of a smaller band than the PCR value of thereceived line “EN” in descending order (step 409).

[0176] At the outset, a judgment is made on whether or not the linehaving the PCR value can be received in the computed idle area (steps410 and 411) when the judgment is such that the line can be received,the allocation position and the idle area are updated (step 412)followed by the cataloging of the position as the allocation position“FEP” of the line having the PCR value “EN” in the schedule managementtable (step 413).

[0177] In the case where the judgment on whether or not the line can bereceived is such that the receive is impossible and, at the same time,the connection has been judged to be final (that is, the PCR value is“1”) (step 414), the total number of used entries “TUEN” and the finalbox number “TUEB” are updated (step 415) to complete the line receiveprocessing.

[0178] Next, the operation in the delete of a line will be explainedwith reference to the flow ehart shown in FIG. 11.

[0179] In the operation in the delete of a line, the line requested tobe deleted is first deleted from the allocation position of the line“SOE” (step 501).

[0180] Next, the allocation move processing of the scheduled lineswithin the cell read sequence management table upon the delete of a linewill be explained in various classified cases.

[0181] Here a judgment is made on whether or not an idle areacorresponding to the deleted line is present within the cell readmanagement table (stop 503). When the judgment is such that the idlearea is present, a position correction value derived from the locationmovement is computed as shown in FIG. 13 (steps 504 to 507). Here theidle area corresponding to the line is in a state shown in FIG. 13according to the condition in the step 505. Therefore, the allocationposition after the location movement is corrected as indicated in thestep 506 or step 507.

[0182] After the computation of the position correction value, theobject line is corrected as shown in FIG. 14 (steps 508 and 509) In thiscase, the condition in the step 508 is established when the length ofthe line to be moved is identical to the length of the deleted line.When the condition in the step 508 is not established, branching isperformed without the movement of the line.

[0183] When the location move processing has been carried out, due tothe update of the cell read sequence management table caused by thelocation movement, the values of the schedule management table areupdated as shown in FIG. 15 (steps 510 to 516). In the update of theschedule management table, when the position of an idle area has beenmoved by the move processing (steps 511 and 512), the allocationposition within the schedule management table is corrected (step 513).The above update is sequentially carried out in the descending order ofPCR values of lines (step 515).

[0184] After the completion of the move processing, a larger idle areais ensured, and, consequently. in some cases, the location movement of alarger-band line can be realized. In this case, the PCR value of theline is updated, and the above procedure is then repeated (step 516).

[0185] In the branch in the step 503, when any idle area correspondingto the object line is not present within the cell read sequencemanagement table, the next line receive position is updated (step 517),and a judgment on location movement is made (step 518). Specifically, inthe case where, after the line delete processing (step 518), thelocation movement of the line is impossible and there is no change inthe final box number “TUEB,” the total number of used entries is updatedto complete line delete processing (step 528).

[0186] On the other hand, when the delete of a line is accompanied bylocation movement, the move processing is carried out (step 520). Inthis case, howcver, when the object line to be deleted is located at therear end of the final box number, the move processing is not carried out(step 519). The update of the schedule management parameters after thelocation move processing (steps 521 to 526) is the same as that in thesteps 510 to 516.

[0187] After the completion of the update of the schedule managementparameters, the total number of used entries “TUEN” and the final boxnumber “TUEB” are updated to complete the line delete processing (step527).

[0188] As explained above, according to the scheduling system of thispreferred embodiment, the position of individual lines in the cell readsequence management table can be properly allocated by simpleprocessing.

[0189] In the present preferred embodiment, the conversion methodexemplified in FIGS. 2 and 3 is used in the conversion of the lines,located at the respective positions in the cell read sequence managementtable, to a time slot. However, when the lines are continuously ensuredfrom a position which is one ahead of the position corresponding to avalue obtained by multiplying the PCR value by an integer, theconversion method for dispersing the ensured elements at equal spacingsin the timc slot is not limited to the method shown in FIGS. 2 and 3,and FIGS. 2 and 3 merely illustrate one example of possible conversionmethods.

[0190] In this connection, it should be noted that, in all theabove-described examples, the scheduling method for a cell read sequencemanagement table according to the scheduling system of the presentpreferred embodiment is not influenced by the method for convertinglines to a time slot, and the same effect can be attained even whenother conversion methods satisfying the above requirement for conversionto a time slot are adopted.

[0191] As described above, the scheduling system according to theinvention has the following effects.

[0192] According to the scheduling system of the invention, in a cellread sequence management table for assuring the rate of ATM lines andmanaging the transfer of cells, making reference to a schedulemanagement table permits the position of each line to be properlydetermined based on the PCR value of the line. Therefore, in thescheduling system of the invention, satisfying the requirements whichhave been necessary in the prior art technique, for example, therequirement for alignment in the descending order of PCR values and therequirement for the avoidance of the creation of any idle area betweenlines, is not required, and, thus, in the invention, scheduling can berealized in a proper and more flexible manner.

[0193] In the conventional scheduling system, in order to assure therate of individual ATM lines, for example, in newly receiving a line ordeleting a line, scheduling should be carried out in the descendingorder of PCR values and so that no idle area is provided between lines.For this reason, in the prior art technique, every time when the receiveof a new line, the delete of a line or the like had occurred,troublesome update processing should be carried out wherein theindividual lines are aligned and rearranged.

[0194] The use of the scheduling system according to the invention cansubstantially eliminate the need to perform alignment and otherprocessing every time, for example, when a line has been newly received.

[0195] Processing, in the case where newly receiving a line and deletinga line are repeatedly carried out, according to the invention may becompared with processing, in the case where newly receiving a line anddeleting a line are repeatedly carried out, according to the prior arttechnique by comparing FIG. 16 (invention) with FIG. 1 (prior arttechnique). In both FIGS. 16 and 1, identical processings for the add ordelete of connection indicated from the top to the bottom in theleft-side column are carried out. The comparison shows that, in thescheduling system according to the invention, the number of objects tobe location moved is significantly reduced as compared with that in theprior art technique.

[0196] For example, in newly receiving a line, in the prior arttechnique, a part of other connections having a PCR value equal to thecontemplated connection and all of connections having a smaller PCRvalue than the contemplated connection should be moved, whereas, in thescheduling system according to the invention, there is no need to movethe connections.

[0197] On the other hand, in deleting a line, in the prior art, a partof other connections having a PCR value equal to the contemplatedconnection and all of connections having a smaller PCR value than thecontemplated connection should be moved, whereas, in the schedulingsystem according to the invention, what is required is only to move oneconnection having a PCR value equal to or larger than the contemplatedconnection.

[0198] Further, also in the unused (free) area within the cell readsequence management table, the invention has no disadvantage over theprior art technique.

[0199] This is apparent from FIG. 16 (example of invention) and FIG. 1(example of prior art) which each show a table illustrating conversionto the number of lines having PCR values obtained by raising 2 to thenth power, wherein n is an integer, in the unused area within the cellread sequence management table. The comparison of FIG. 16 with FIG. 1shows that, in the scheduling system according to the invention, thesame quantity of line as the prior art technique can be newly receivedin each step of this example.

[0200] As is apparent from the foregoing description, the use of thescheduling system according to the invention can significantly reducethe processing necessary for scheduling while realizing the same linecapacity as the prior art technique.

[0201] The invention has been described in detail with particularreference to preferred embodiments, but it will be understood thatvariations and modifications can be effected within the scope of theinvention as set forth in the appended claims.

What is claimed is:
 1. A scheduling system comprising: a time slot forspecifying the transfer sequence of individual lines in one turn, inwhich each cell is transferred, in slots indicating respective points inthe turn; a cell read sequence management table which has elements inthe same number as the number of slots provided in the time slot andsets the lines as cell transfer objects to the elements; schedulecomputation means for controlling the setting of the lines to the cellread sequence management table; allocation processing means forconverting the elements of the cell read sequence management tablerespectively to specified positions of the slots in the time slot; and aschedule management table for indicating positions, within the cell readsequence management table, to which transfer object lines are newly set,for each PCR value of the lines, said PCR value being the number ofcells, transferred from the line, per cell transfer turn andrepresenting the cell send rate of each line, the specified line cellsbeing successively transferred for each turn according to the sequencespecified in the time slot, the cell read transfer sequence in each linebeing controlled according to the cell send rate in each of the lines.2. The scheduling system according to claim 1, wherein the schedulecomputation means comprises; means which, when a requirement issatisfied such that there is an idle element, in the cell read sequencemanagement table, which is located one element ahead of a position of anelement corresponding to a value obtained by multiplying the specifiedPCR value by an integer, and the contemplated line can be set tocontinuous elements starting from the idle element and corresponding tothe specified PCR value and, in addition, when an element is present inthe heading area of the continuous elements, functions to catalog theposition of said element, which is located one element ahead of aposition of an element corresponding to a value obtained by multiplyingthe specified PCR value by an integer, as data indicating the setposition of the line having the specified PCR value, in relation withthe PCR value in the schedule management table; means which, when a lineto be newly transferred has is occurred, newly sets the line tocontinuous elements corresponding to the PCR value of the line, in thecell read sequence management table, from the set position correspondingto the PCR value of the line recorded in the schedule management table;means which, when the communication of a line being currentlytransferred has been deleted, cancels the setting of the line from theelement, in the cell read sequence management table, to which the linehas been set; and means which, when new setting or delete of a transferobject line has occurred, updates the catalog of the schedule managementtable.
 3. The scheduling system according to claim 2, wherein theallocation processing means comprises: means which converts the elementswithin the cell read sequence management table, to respective specifiedpositions within the time slot, based on the designation of the slotposition as the conversion destination for each element specified insuch a manner that the continuous elements corresponding to the PCRvalue, that have been ensured from a position which is one element aheadof a position of an element corresponding to a value obtained bymultiplying the PCR value by an integer, in the cell read sequencemanagement table are converted to respective positions dispersed atequal spacings in the time slot; and means which, when a line is in thestate of being set to elements in the cell read sequence managementtable, performs specifying and setting, in a slot as the conversiondestination of the line in the time slot, so as to transfer cells of theline.
 4. The scheduling system according to claim 2 or 3, wherein thenumber of slots in the time slot and the PCR value of each of the lineseach are a value obtained by raising “2” to the nth power, wherein n isa non-negative integer.
 5. The scheduling system according to claim 4,wherein the conversion from the cell read sequence management table tothe time slot is carried out by a method comprising the steps of:raising “2” to the “Ath” power, wherein “A” is an integer, to provide avalue as the length of the time slot; indicating the positions of theindividual elements in the cell read sequence management table and theslot positions of the time slot by using continuous numbers from “1” tothe value of the time slot length; taking each element from the cellread sequence management table; subtracting “1” from the value of thecontinuous numbers in the element and expressing the obtained value interms of binary number of “A” digits while, when a high order value isabsent, supplementing “0”; converting the numerical values of the “A”digits expressed in terms of binary number so as to be reversed insequence with respect to the arrangement from higher order digit tolower order digit to provide a converted binary number of “A” digits;and adding “1” to the value of the converted binary number of “A” digitsto determine a value as a slot position, in the time slot, which is theelement conversion destination.
 6. The scheduling system according toany one of claims 2 to 5, wherein the schedule computation meansperforms a function such that, upon the cancellation of the setting of aline from the elements in the cell read sequence management table, ifanother line having a smaller PCR value than said line is in the stateof being set to a position behind the position to which the said linehas been set, the set position of said another line is moved to theposition from which the setting of said line has been cancelled.
 7. Thescheduling system according to any one of claims 2 to 5, wherein theschedule computation means performs a function such that, upon thecancellation of the setting of a line from the elements in the cell readsequence management table, if other lines having a smaller PCR valuethan said line are in the state of being set to positions behind theposition to which the said line has been set, the set position of oneline, which has the largest PCR value in said other lines and is locatedin the rearmost position of said other lines, is moved to the positionfrom which the setting of said line has been cancelled.
 8. Thescheduling system according to any one of claims 1 to 7, wherein saidline is an ATM line.
 9. A scheduling method comprising the steps of;indicating the send rate of cells in each line in terms of PCR valuewhich is the number of calls, transferred from the line, per celltransfer turn; successively transferring cells of a specified lineaccording to the sequence specified in slots, in a time slot forspecifying the transfer sequence of individual lines in the celltransfer turn, indicating each point in the turn; controlling thesetting of each line in a cell read sequence management table which haselements in the same number as the number of slots provided in the timeslot and sets the lines as cell transfer objects to the elements;converting the individual elements in the cell read sequence managementtable to respective specified slot positions in the time slot; andproperly updating and making reference to a schedule management tablewhich indicates positions, within the cell read sequence managementtable, to which transfer object lines are newly set, for each PCR valueof the lines, the cell read transfer sequence in each line beingcontrolled according to the cell send rate in each of the lines.
 10. Thescheduling method according to claim 9, which further comprises thesteps of: when a requirement is satisfied such that there is an element,in the cell read sequence management table, which is located one elementahead of a position of an element corresponding to a value obtained bymultiplying the specified PCR value by an integer, and the contemplatedline can be set to continuous elements starting from the idle elementand corresponding to the specified PCR value and, in addition, when anelement is present in the heading area of the continuous elements,cataloging the position of said element, which is located one elementahead of a position of an element corresponding to a value obtained bymultiplying the specified PCR value by an integer, as data indicatingthe set position of the line having the specified PCR value within thecell read sequence management table, in relation with the PCR value inthe schedule management table; when a line to be newly transferred hasoccurred, newly setting the line to continuous elements corresponding tothe PCR value of the line, in the cell read sequence management table,from the set position corresponding to the PCR value of the linerecorded in the schedule management table; when the communication of aline being currently transferred has been deleted, canceling the settingof the line from the element, in the cell read sequence managementtable, to which the line has been set; and when new setting or delete ofa transfer object line has occurred, updating the catalog of theschedule management table.
 11. The scheduling method according to claim10, which further comprises the steps of; converting the elements withinthe cell read sequence management table, to respective specifiedpositions within the time slot, based on the designation of the slotposition as the conversion destination for each element specified insuch a manner that the continuous elements corresponding to the PCRvalue, that have been ensured from a position which is one element aheadof a position of an element corresponding to a value obtained bymultiplying the PCR value by an integer, in the cell read sequencemanagement table are converted to respective positions dispersed atequal spacings in the time slot; and when a line is in the state ofbeing set to elements in the cell read sequence management table,performing specifying and setting, in a slot as the conversiondestination of the line in the time slot, so as to transfer cells of theline.
 12. The scheduling method according to claim 10 or 11, wherein thenumber of slots in the time slot and the PCR value of each of the lineseach are a value obtained by raising “2” to the nth power, wherein n isa non-negative integer.
 13. The scheduling method according to claim 12,wherein the conversion from the cell read sequence management table tothe time slot is carried out by a method comprising the steps of:raising “2” to the “Ath” power, wherein “A” is an integer, to provide avalue as the length of the time slot; indicating the positions of theindividual elements in the cell read sequence management table and theslot positions of the time slot by using continuous numbers from “1” tothe value of the time slot length; taking each element from the cellread sequence management table; subtracting “1” from the value of thecontinuous numbers in the element and expressing the obtained value interms of binary number of “A” digits while, when a high order value isabsent, supplementing “0”; converting the numerical values of the “A”digits expressed in terms of binary number so as to be reversed insequence with respect to the arrangement from higher order digit tolower order digit to provide a converted binary number of “A” digits;and adding “1” to the value of the converted binary number of “A” digitsto determine a value as a slot position, in the time slot, which is theelement conversion destination.
 14. The scheduling method according toany one of claims 10 to 13, wherein, upon the cancellation of thesetting of a line from the elements in the cell read sequence managementtable, if another line having a smaller PCR value than said line is inthe state of being set to a position behind the position to which thesaid line has been set, the set position of said another line is movedto the position from which the setting of said line has been cancelled.15. The scheduling method according to any one of claims 10 to 13,wherein, upon the cancellation of the setting of a line from theelements in the cell read sequence management table, if other lineshaving a smaller PCR value than said line are in the state of being setto positions behind the position to which the said line has been set,the set position of one line, which has the largest PCR value in saidother lines and is located in the rearmost position of said other lines,is moved to the position from which the setting of said line has beencancelled.
 16. The scheduling method according to any one of claims 9 to15, wherein said line is an AMT line.
 17. An ATM switch comprising ascheduling system such that the cell read transfer sequence in each ATMline is controlled according to the cell send rate in each of the ATMlines, wherein said scheduling system expresses the cell send rate, ineach of the ATM lines, in terms of PCR value, which is the number ofcells, transferred from the ATM line, per cell transfer turn andcomprises: a time slot for specifying the transfer sequence of the ATMlines in one turn, in which each cell is transferred, in slotsindicating respective points in the turn; a cell read sequencemanagement table which has elements in the same number as the number ofslots provided in the time slot and sets the ATM lines as cell transferobjects to the elements; schedule computation means for controlling thesetting of the ATM lines to the cell read sequence management table;allocation processing means for converting the elements of the cell readsequence management table respectively to specified positions of theslots in the time slot; and a schedule management table for indicatingpositions, within the cell read sequence management table, to whichtransfer object ATM lines are newly set, for each PCR value of the ATMlines, the specified ATM line cells being successively transferred foreach turn according to the sequence specified in the time slot.
 18. TheATM switch according to claim 17, wherein the schedule computation meanscomprises: means which, when a requirement is satisfied such that thereis an idle element, in the cell read sequence management table, which islocated one element ahead of a position of an element corresponding to avalue obtained by multiplying the specified PCR value by an integer, andthe contemplated ATM line can be set to continuous elements startingfrom the idle element and corresponding to the specified PCR value and,in addition, when an element is present in the heading area of thecontinuous elements, functions to catalog the position of said element,which is located one element ahead of a position of an elementcorresponding to a value obtained by multiplying the specified PCR valueby an integer, as data indicating the set position at the ATM linehaving the specified PCR value, in relation with the PCR value in theschedule management table; means which, when an ATM line to be newlytransferred has occurred, newly sets the ATM line to continuous elementscorresponding to the PCR value of the ATM line, in the cell readsequence management table, from the set position corresponding to thePCR value of the ATM line recorded in the schedule management table;means which, when the communication of an ATM line being currentlytransferred has been deleted, the setting of the ATM line is cancelledfrom the element, in the cell read sequence management table, to whichthe ATM line has been set; and means which, when new setting or deleteof a transfer object ATM line has occurred, updates the catalog of theschedule management table.
 19. The ATM switch according to claim 18,wherein the allocation processing means comprises: means which convertsthe elements within the cell read sequence management table, torespective specified positions within the time slot, based on thedesignation of the slot position as the conversion destination for eachelement specified in such a manner that the continuous elementscorresponding to the PCR value, that have been ensured from a positionwhich is one element ahead of a position of an element corresponding toa value obtained by multiplying the PCR value by an integer, in the cellread sequence management table are converted to respective positionsdispersed at equal spacings in the time slot; and means which, when anATM line is in the state of being set to elements in the cell readsequence management table, performs specifying and setting, in a slot asthe conversion destination of the ATM line in the time slot, so as totransfer cells of the ATM line.
 20. The ATM switch according to claim 18or 19, wherein the number of slots in the time slot and the PCR value ofeach of the ATM lines each are a value obtained by raising “2” to thenth power, wherein n is a non-negative integer.
 21. The ATM switchaccording to claim 20, wherein the conversion from the cell readsequence management table to the time slot is carried out by a methodcomprising the steps of: raising “2” to the “Ath” power, wherein “A” isan integer, to provide a value as the length of the time slot;indicating the positions of the individual elements in the cell readsequence management table and the slot positions of the time slot byusing continuous numbers from “1” to the value of the time slot length;taking each element from the cell read sequence management table;subtracting “1” from the value of the continuous numbers in the elementand expressing the obtained value in terms of binary number of “A”digits while, when a high order value is absent, supplementing “0”;converting the numerical values of the “A” digits expressed in terms ofbinary number so as to be reversed in sequence with respect to thearrangement from higher order digit to lower order digit to provide aconverted binary number of “A” digits; and adding “1” to the value ofthe converted binary number of “A” digits to determine a value as a slotposition, in the time slot, which is the element conversion destination.22. The ATM switch according to any one of claims 18 to 21, wherein theschedule computation means performs, a function such that, upon thecancellation of the setting of an ATM line from the elements in the cellread sequence management table, if another ATM line having a smaller PCRvalue than said ATM line is in the state of being set to a positionbehind the position to which the said ATM line has been set, the setposition of said another ATM line is moved to the position from whichthe setting of said ATM line has been cancelled.
 23. The ATM switchaccording to any one of claims 18 to 21, wherein the schedulecomputation means performs a function such that, upon the cancellationof the setting of an ATM line from the elements in the cell readsequence management table, if other ATM lines having a smaller PCR valuethan said ATM line are in the state of being set to positions behind theposition to which the said ATM line has been set, the set position ofone ATM line, which has the largest PCR value in said other ATM linesand is located in the rearmost position of said other ATM lines, ismoved to the position from which the setting of said ATM line has beencancelled.